Biological contributions of articular chondrocytes to degenerative joint disease and disturbed skeletal growth are studied by organ and cell culture of cartilage. Phenotypic glycosaminoglycan and collagen synthesis is expressed in organ culture but not under monolayer conditions. Although adult articular chondrocytes do not ordinarily divide in intact cartilage, they grow out from the margin of the latter when explanted into culture medium. Two principal questions are to be explored during the next phase of the investigations: 1) does a DNA repair synthetic mechanism operate to maintain the genetic integrity of the non-replicating chondrocytes of adult articular cartilage throughout its life span? 2) Does senescence of articular chondrocytes occur at a cellular level with advancing years and so account for the age-dependency of osteoarthritis? Autoradiography with 3(H) thymidine following ultraviolet light and X-irradiation of cultured articular cartilage and chondrocytes will be the principal tool for studying unscheduled DNA synthesis. Controlled enzymatic alteration of the permeability of the matrix and the influence of agents that promote scheduled DNA synthesis (platelet growth factor, pituitary chondrocyte growth factor and ascorbate) will be tested in relation to both questions.